In the operation of a vehicle having a plurality of hydraulically operated work elements, as for example an excavator, when the piston of one of the work elements bottoms out, the hydraulic system pressure increases to the setting of the main pressure relief valve of the hydraulic system. It is therefore desirable to provide means associated with each working element to separately control the maximum pressure buildup of each working element and its hydraulic system. By constructing apparatus of this invention to maintain a pressure not greater than a preselected operating pressure for each working element, waste of energy and materials is reduced. Each working element can be constructed to withstand and operate at only the maximum operating pressure that will be subjected onto that particular working element.
This invention therefore resides in apparatus for reducing waste by separately controlling the maximum operating pressure of separate portions of the fluid system serving separate work elements of the vehicle.